The hot gas path components of gas turbine engines are often formed of superalloy materials. The term “superalloy” is used herein as it is commonly used in the art; i.e., a highly corrosion and oxidation resistant alloy that exhibits excellent mechanical strength and resistance to creep at high temperatures. Superalloys typically include a high nickel or cobalt content. Examples of superalloys include alloys sold under the trademarks and brand names Hastelloy, Inconel alloys (e.g. IN 738, IN 792, IN 939), Rene alloys (e.g. Rene N5, Rene 80, Rene 142), Haynes alloys, Mar M, CM 247, CM 247 LC, C263. 718, X-750, ECY 768, 282, X45, PWA 1483 and CMSX (e.g. CMSX-4) single crystal alloys.
Modern gas turbine engines have firing temperatures that exceed the safe operating temperatures of known superalloy materials, so components such as combustors, transitions, and early row rotating blades and stationary vanes are often further protected by a thermal barrier coating applied to the exposed surface of the superalloy material. One such thermal barrier coating system includes a metallic bond coat, such as an MCrAlY material, applied to the superalloy material and overlaid by a ceramic insulating material such as yttria stabilized zirconia (YSZ).
The thermal barrier coatings of gas turbine engine components are known to suffer degradation such as erosion, corrosion, oxidation, cracking, spallation, etc. during operation of the engine. Particular areas of particular components may be most susceptible to degradation, such as the leading edge of an airfoil, or the platform or tip of a rotating blade. Engines are periodically dismantled and inspected, and degraded components are removed for refurbishment or replacement as appropriate. A degraded area of thermal barrier coating material may be removed by mechanical or chemical means, the underlying substrate material inspected and repaired as appropriate, and a fresh thermal barrier coating applied. The component may also be subjected to a solution heat treatment in order to restore the mechanical properties of the superalloy material. Examples of known thermal barrier coating materials and repair processes can be found in: U.S. 6,042,880 A (Rigney, et al.); EP 2233450 A1(Alstom Technology Limited); U.S. 6,210,812 (Hasz, et al.); and JP 2012 112290 A (Toshiba Corporation).